The present invention relates to one component silicone compositions which cure at room temperature to form elastomeric type products. More particularly the present invention relates to room temperature vulcanizable. (RTV) silicone rubber compositions with improved adhesion to acrylic substrates.
The composition of the present invention is a one component RTV silicone composition comprising: (A) hydroxyl endblocked polyorganosiloxane, (B) at least one phenyl substituted tris-functional ketoximino silane and (C) an aminofunctional silane adhesion promoter which is characterized as having less than three hydrolyzable alkoxy groups attached to silicon or Si.
The sealant composition of the present invention contains (A) hydroxyl endblocked diorganosiloxane as a basic ingredient which may have a viscosity generally between about 100 to about 500,000 centipoise at 25xc2x0 C., preferably from about 2000 to about 350,000 centipoise, and most preferably between about 2000 and about 150,000 centipoise. These diorganosiloxane polymers are well-known in the art. The polymer may have the following general formula: 
where n varies such that the viscosity of the polymer varies from 100 to 500,000 centipoise. The organo groups can be monovalent hydrocarbon radicals or monovalent halogenated carbon radicals. Examples of such monovalent hydrocarbon radicals are methyl, ethyl, propyl, butyl, phenyl, methylphenyl, ethylphenyl, vinyl, allyl, cyclohexyl, tolyl, and isopropyl. Examples of monovalent halogenated hydrocarbon radicals are chloropropyl, 3,3,3-trifluoropropyl, chlorophenyl, beta- (perfluorobutyl)ethyl, and chlorocyclohexyl. Preferably the organic radicals are methyl, ethyl, phenyl, vinyl, and 3,3,3-trifluoropropyl. The polydiorganosiloxane can have in addition to the diorganosiloxane units, mono-organosilsesquioxane units, triorganosiloxy units, and Si02 units. Polydiorganosiloxanes which have both hydroxyl endblocking and triorganosiloxy endblocking may also be used and are described in U.S. Pat. No. 3,274,145 by Dupree, which is incorporated herein by reference. Component (A) can be a mixture of two or more polyorganodisiloxanes as long as the average viscosity of the mixture falls within the viscosities stated above. The preferred hydroxy terminated polydiorganosiloxane polymer has methyl as the organic substituent on the polymer backbone and is available from a number of sources such as General Electric, blacker Silicones, Shin-Etsu Silicones and Dow Corning.
The amount of polymer (A) to be used in this invention ranges from about 15 to about 95 percent by weight of the total composition, preferably, from about 30 to about 85 percent by weight of the total composition and most preferably about 30 to about 75 percent by weight of the composition.
The trifunctional crosslinking agent (B) has the formula: Rxe2x80x94Si(ONxe2x95x90CRxe2x80x22)3 where R is phenyl. Rxe2x80x2 may be any saturated straight chain or branched alkyl radical of from about 1 to about 8 carbon atoms. Methods for the preparation of such ketoximino silanes are known in the art. See U.S. Pat. No. 4,380,660 and U.S. Pat. No. 4,400,527 to Matthew. These patents as well as U.S. Pat. No. 3,186,576 to Sweet disclose the various ketoximes which can be used in this invention. The above patents are incorporated herein by reference. Illustrative of some of these ketoximes are methyl ethyl ketoxime, diethylketone oxime, acetone oxime, methyl isobutyl ketoxime, methyl amyl ketoxime, and cyclohexanone oxime. Because of the relative availability of methyl ethyl ketoxime and methyl isobutylketoxime, the preferred silane crosslinking agents (B) in this invention are phenyl tris-(methyl ethyl ketoximino) silane or phenyl tris-(methyl isobutylketoximino) silane. Phenyl tris-(methyl ethyl ketoximino) silane is commercially available from Honeywell International Inc. of Morristown, N.J. Crosslinker (B) is generally present in an amount of from about 1 to about 10 percent by weight of the total composition, and preferably from about 2 to about 7 percent by weight of the total composition, and most preferably from about 3 to about 6 percent by weight of the total composition.
Although it is preferred that crosslinker (B) is the sole crosslinker used in this invention, in another embodiment of the invention mixtures of phenyl substituted tris functional silanes are employed. In still another embodiment, at least one phenyl substituted tris functional silane is used with small amounts of other crosslinkers. These other crosslinkers are well known in the art and include methyltrimethoxysilane, vinyl trimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, methyltriacetoxysilane, ethyltriacetoxysilane, methyl tris-(N-methylbenzamido) silane, methyl tris(isopropenoxy) silane, and methyl tris-(cyclohexylamino) silane, methyl tris(methyl ethyl ketoxirino) silane, vinyl tris-(methyl ethyl ketoximino) silane, methyl tris-(methyl isobutyl ketoximino) silane, vinyl tris-(methyl isobutyl ketoximino) silane, tetrakis-(methyl ethyl ketoxirino) silane, tetrakis(methyl isobutyl ketoximino) silane, and tetrakis-(methyl amyl ketoximino) silane. Difunctional ketoximino silanes may also be used such as dimethyl di(methyl ethyl ketoximino) silane, methyl vinyl di-(methyl ethyl ketoximino) silane, methyl vinyl di-(methyl isobutyl ketoximino) silane, and methyl vinyl di-(methyl amyl ketoximino) silane.
Tetrafunctional alkoxy-ketoxime silanes as disclosed by Klosowski U.S. Pat. No. 15 4,657,967 and Haugsby U.S. Pat. No. 4,973,623 can also be used to modulate cure speed of the present invention. Similarly other tetrafunctional alkoxy-ketoximino silanes as described in U.S. patent application Ser. Nos. 947,015 filed Sep. 17, 1992; 143,777 filed Nov. 1, 1993 and 158,660 filed Nov. 29,1993 can be used. All of the above crosslinkers may be added as mixtures with crosslinker (B) or added separately to the composition of this invention. It is preferable that any auxiliary crosslinkers used not exceed about 25 percent by weight of the total crosslinker level. Using crosslinkers other than (B) in increasing amounts, in conjunction with (B) generally increases the modulus and decreases the elongation of the cured composition of the invention and decreases the adhesion of the sealant or coating to acrylic substrates. Crosslinker (B) as well as other crosslinkers used can be added to (A) before the addition of other ingredients under.anhydrous conditions.
The composition of the present invention contains an adhesion promoter (C) which is characterized as having an amino functional group and less than three hydrolyzable alkoxy groups attached to silicon or Si. N-(2-aminoethyl)3-aminopropylmethyldimethoxy silane, gamma-aminopropylmethyldiethoxysilane, gamma-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3aminopropylmethyldiethoxy and mixtures thereof are examples of aminofunctional silanes with two hydrolyzable alkoxy groups which provide adhesion to acrylic. These promoters are generally used in an amount of from about 0.1 to about 3 percent by weight of the total composition. Preferably from about 0.2 to about 2.5 percent by weight of the total composition and most preferably from about 0.5 to about 1.5 percent by weight of the total composition. N-(2-aminoethyl)3-aminopropylmethyldimethoxy silane is available from Witco, Huls/Degussa, and Shin-Etsu while gamma-aminopropylmethyldiethoxysilane is available from Huls and gamma-aminopropylmethyldimethoxysilane is available from Silar Industries. Although it is contemplated that N-(2-aminoethyl)-3aminopropylmethyldiethoxy provides good adhesion, there is no commercial source for this material today. However, it can be prepared by adapting the method disclosed in Japanese application, JP 92-7593, to Shinetsu Chemical Ind. for the production of N-(aminoethyl)-3-aminopropylmethyldimethoxysilane Essentially,, one would react 1 equivalent of 3-chloropropylmethyldiethoxysilane is reacted with 3-5 equivalents of ethylenediamine. This material may also be prepared by using methyldichlorosilane hydrosilylation with 3-chloropropene, then reacting the product with ethanol and ethylenediamine per the publication by Jiangxi Normal University Department of Chemistry (Peng, Yiyuan; Mao, Xuechan et al.) 1998.
While the basic embodiment of the invention utilizes one adhesion promoter of the invention in the composition, in another embodiment, mixtures of adhesion promotors of the invention (i.e., containing an amino functional group and less than three hydrolyzable alkoxy groups attached to silicon) can be used to obtain optimal adhesion to acrylic. In still another embodiment of the invention, at least one adhesion promoter of the invention is used with still other adhesion promoters to obtain an improvement in various other properties of the composition such as improved resistance to hydrolysis or improved adhesion to other surfaces. Typically these adhesion promoters can be chosen from many organofunctional silanes known in the art. A nonexhaustive list of such silanes include gamma-aminopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, trimethoxysilylpropyldiethylene triamine, bis-(gammatrimethoxysilylpropyl)amine, gamma-ureidopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxy silane, beta-(3,4-epoxycyclohexyl) ethyltrimethoxysilane, tris-[3-(trimethoxysilyl)propyl] isocyanurate, gammaglycidoxypropylmethyldiethoxysilane, N-phenyl-gamma-aminopropyltrimethoxy silane, gamma-mercaptopropyltrimethoxysilane, and gamma-methacryloxypropyltrimethoxysilane.
Preferably the optional adhesion promotors are present in an amount of from about 0.2 to about 1.0 percent by weight of the total composition. However as the presence or level of the optional adhesion promoters,increases, the adhesion to acrylic is usually decreased. Thus only a minimum level of the optional adhesion promoters is desired to achieve the overall balance of desired properties. These adhesion promoters can be obtained from a number of sources such as Huls/Degussa, Witco, Shin-Etsu and Dow Corning Corp.